The invention relates to optical communications. More particularly, the invention relates to a variable attenuator for optical communications.
Optical attenuators are used to optimize the optical power of signals at key points in optical communications networks. For example, in networks having Erbium Doped Fiber Amplifiers (EDFAs), optical attenuators are used between stages of EDFAs to provide constant gain. In Wavelength Division Multiplexed (WDM) systems, optical attenuators are used to adjust optical power of xe2x80x9caddedxe2x80x9d laser signals to match the signal strength of other channels within the network. Optical attenuators can also be used to set signal strength within the range of a particular receiver.
In order to optimize signal strength in fiber optic networks, fiber optic attenuators have been developed. For example, U.S. Pat. No. 5,087,122 issued to Ostrander, et al. (the ""122 patent) discloses a blocking beam type attenuator. The ""122 patent discloses a vane-line mechanical blocker that is gradually rotated in to a collimated beam to cause light attenuation. The attenuator of the ""122 patent provides low insertion loss, low polarization dependent loss, and low wavelength dependent loss.
However, compact size is desired for most fiber optic components. The attenuator of the ""122 patent is not compact in size. Further, the attenuator of the ""122 patent provides a full range of attenuation over a small angle of rotation. Thus, the attenuator of the ""122 patent requires precise control, which increases manufacturing costs. What is needed is an improved attenuator for use with fiber optic communications signals.
A variable fiber optic attenuator is described. The attenuator includes an input port to receive an optical signal. The attenuator can also include an output port that receives an attenuated version of the input signal and causes the attenuated signal to focus on an output device (e.g., an optical fiber). A special profile blocker is used to attenuate the optical signal resulting in an attenuated optical signal. In one embodiment, the special profile blocker is an eccentrically driven wheel. In an alternative embodiment, the special profile blocker is a cam with a radius that gradually changes angularly.